1. Field of the Invention
The present invention relates to a cooling device which is used to reduce the temperature caused by heat generated, e.g., from a driver of a card type memory medium used in a personal computer, a digital camera, or the like, and to a method of producing the same. Moreover, the present invention relates to an electronic apparatus such as a personal computer, a digital camera, or the like, on which the cooling device is mounted.
2. Description of the Related Art
Storage media such as Memory Stick (registered trademark), Smart Media (registered trademark), Compact Flash (registered trademark), and so forth are small in size and thickness, and also the storage capacities can be considerably increased compared to conventional storage media such as Floppy (registered trademark) disks or the like. Thus, they have been generally used in electronic apparatuses such as personal computers, digital cameras, and so forth. Regarding some of these storage media, flash memories integrated with drivers are used, or drivers are mounted on the main parts of apparatuses, other cards, or the like. For the storage media, recently, the capacities have been significantly increased. With increasing of the storage capacities of the storage media as described above, problems have arisen in that much heat is generated to cause defects in operation.
Accordingly, it has been proposed that a cooling device is provided for a heat source in such an apparatus. For example, a cooling method using a heat pipe has been proposed.
A heat pipe is a metallic pipe of which the inner wall has a capillary structure, of which the inside is evacuated, and which tightly contains a small amount of water or a substitution Freon therein. When one end of the heat pipe is brought into contact with a heat source to be heated, the liquid contained therein is evaporated. Then, heat is taken into the gas as latent heat (evaporation heat). The heat is transferred to a low temperature region at a high speed (substantially equal to a sound velocity). The gas is cooled to be returned to the liquid, and the heat is released (the heat is released due to the condensation latent heat). The liquid is passed through the capillary structure (or due to the gravity) to be returned to its original position. Thus, the heat can be efficiently transferred.
However, the related art heat pipe is tubular and voluminous. Accordingly, the heat pipe is unsuitable as a cooling device for use in electronic apparatuses such as personal computers, digital cameras, and so forth for which reduction of the size and the thickness is required.
Accordingly, to reduce the size of the heat pipe, a cooling device has been proposed in which grooves are formed on the surface of a silicon substrate and that of a glass substrate to be joined to each other, and these substrates are joined to form the flow-path of a heat pipe between the substrates. When the joining is carried out, a small amount of water or a substitution Freon is introduced to be tightly kept. The phase of the water or Freon is changed in the heat pipe, so that the function of the heat pipe can be performed.
However, in the case in which the heat pipe is formed by use of a silicon substrate as described above, heat from an object to be cooled is diffused, since the thermal conductivity of the silicon itself is high. Thus, there are problems in that the evaporation of a liquid in the heat pipe is insufficient, or the evaporation is not caused at all, so that the function of the heat pipe can not be carried out.
Moreover, electronic apparatuses having silicone substrates mounted thereon have problems in that they may be broken in event that the apparatuses drop.
Accordingly, it is an object of the present invention to provide a cooling device of which the cooling performance, the thermal stability, and strength are superior, an electronic apparatus and a display unit each containing the cooling device, and a method of producing the cooling device.
According to a first aspect of the present invention, there is provided a cooling device which comprises a first substrate having grooves constituting a heat pipe formed therein so as to be exposed to the surface thereof, the grooves excluding at least the groove positioned in correspondence to a wick, a second substrate made of a metal or a material having a thermal conductivity substantially equal to that of a metal, the second substrate having at least the groove for the wick formed at the surface thereof, said surface being joined to the first substrate, and a third substrate into which the second substrate is incorporated so as to be exposed to the surface of the third substrate, said surface of the third substrate being joined to the first substrate, at least one of the first substrate and the third substrate being made of a polyimide resin.
According to the present invention, the second substrate having a groove for a wick formed on one side thereof is made of a material having a thermal conductivity substantially equal to a metal. Thus, heat from a heat source can be efficiently transferred to the groove of the wick. On the other hand, the first substrate and so forth are made of a polyimide resin, so that the thermal conductivity is low. Thus, the heat accumulated in the wick is less diffused. Accordingly, the heat is enclosed in the wick, so that the quantity of the latent heat can be substantially increased. Thus, the cooling performance of the heat pipe can be enhanced. In addition, the polyimide resin, which is thermally stable and flexible, is superior in strength. Thereby, the service life of the cooling device can be increased.
Preferably, the fourth substrate of the cooling device having at least a groove for a condenser formed on the surface thereof is made of a metal or a material having a thermal conductivity substantially equal to a metal. Thus, heat from a heat source can be efficiently transferred to the groove of the condenser. On the other hand, the first substrate and so forth are made of a polyimide resin, so that the thermal conductivity is low. Thus, the heat accumulated in the wick is less diffused. Accordingly, the heat is enclosed in the condenser, so that the quantity of the latent heat can be substantially increased. Thus, the cooling performance of the heat pipe can be enhanced.
Preferably, at least one of the second substrate and the fourth substrate is made of a metal containing copper or nickel. Therefore, the heat efficiency is enhanced.
Moreover, a thin film layer made of silicon or copper may be interposed between the one side of the first substrate and the one side of the third substrate. Thereby, the first substrate and the third substrate each made of a polyimide resin can be joined to each other via the thin films of silicon or copper or via an adhesive provided between the thin films. In this case, as the adhesive, a thermoplastic resin such as a thermoplastic polyimide or the like is suitably used.
Preferably, the first substrate and the third substrate joined to each other are physically separated from each other into a region containing the second substrate and a region containing the condenser as a component of the heat pipe, and the cooling device further comprises a flexible substrate interposed between the separated regions and has a flow-path formed therein so as to connect the wick and the condenser to each other. This enables the flow-path substrate for forming a heat pipe to have a flexible shape.
According to a second aspect of the present invention, there is provided a cooling device which comprises a first member having at least a wick as a component of a heat pipe, a second member physically separated from the first member and provided with a condenser as a component of the heat pipe, and a flexible substrate interposed between the first member and the second member and having a flow-path for connecting the wick and the condenser to each other formed therein, at least one of the first member and the second member being made of a polyimide resin. Thus, the wick member and the condenser member can be installed, even if they are not arranged on a plane.
According to a third aspect of the present invention, there is provided a cooling device which comprises: a first substrate having open grooves constituting a heat pipe formed therein, the open groove excluding at least the open groove positioned in correspondence to a wick; a second substrate made of a material having a thermal conductivity substantially equal to that of a metal, the second substrate having at least the groove for the wick formed at the surface thereof, said surface being joined to the first substrate; a third substrate into which the second substrate is incorporated so as to be exposed to the surface of the third substrate, said surface of the third substrate being joined to the first substrate; and a lid-substrate joined to the surface of the first substrate so as to cover said surface which is opposite to the side of the first substrate where the first substrate and the second substrate are joined to each other; at least one of the first substrate, the third substrate, and the lid-substrate being made of a polyimide resin.
Thus, the lid-substrate is brought in close contact with the open grooves of the first substrate, so that the flow-path of a heat pipe can be formed, and the thickness of the first substrate becomes that of the flow-path. Thus, the flow-path is substantially increased in size, so that the performance of the heat pipe is increased.
Preferably, the flow-path for a working fluid, formed by joining of the open grooves of the first substrate and the lid-substrate, has a diamond-like carbon film formed on the inner wall thereof.
In the cooling device of the present invention, at least one of the first substrate, the third substrate and the lid-substrate is made of a polyimide resin. The polyimide resin is water-absorptive to some degree. Accordingly, in the case in which the flow-path for a working fluid is made of a polyimide resin, the durability can be increased by formation of such a diamond-like carbon film on the surface of the flow-path.
According to a fourth aspect of the present invention, there is provided an electronic apparatus which comprises: a slot to or from which a card type storage device containing a flash memory and a driver can be attached or detached; and a cooling device arranged adjacently to the slot, the cooling device comprising a first substrate having grooves constituting a heat pipe formed therein so as to be exposed to the surface thereof, the groove excluding at least the groove positioned in correspondence to a wick, a second substrate made of a metal or a material having a thermal conductivity substantially equal to that of a metal, the second substrate having at least the groove for the wick formed at the surface thereof, said surface being joined to the first substrate, and a third substrate into which the second substrate is incorporated so as to be exposed to the surface of the third substrate, said surface of the third substrate being joined to the first substrate, the first substrate and the third substrate being made of a polyimide resin.
The present invention may be applied as cooling devices for central processing units of note-sizes personal computers, slots for attachment of external storage units, and drivers for liquid crystal display units and so forth. Thereby, the cooling performance of these apparatuses can be enhanced, and moreover, the apparatus can be given a high strength.
According to a fifth aspect of the present invention, there is provided a method of producing a cooling device which comprises the steps of a method of processing a cooling device comprising the steps of forming a first substrate made of a polyimide resin and having grooves constituting a heat pipe formed therein so as to be exposed to the surface thereof, the grooves excluding at least the groove positioned in correspondence to a wick; forming a second substrate made of a metal or a material having a thermal conductivity substantially equal to that of a metal, the second substrate having at least the groove for the wick formed on the surface thereof, incorporating the second substrate into a third substrate so as to be exposed to the surface of the third substrate, and joining the surface of the first substrate to the surface of the third substrate to each other. According to this invention, the cooling device having the above-described structure can be produced efficiently and securely.
Preferably, the method further comprises a step of incorporating the fourth substrate made of a metal or a material having a thermal conductivity substantially equal to that of a metal into the third substrate so as to be exposed to the surface of the third substrate. According to this structure, the condenser section is made of a material having a high thermal conductivity, and thereby, heat can be effectively transferred.
The surface of the first substrate and that of the third substrate may be melt-joined to each other by heating the first and second substrates. Accordingly, the joining can be securely carried out, and the cost reduction becomes possible, due to the simple joining process.
Preferably, the method further comprises a step of forming a diamond-like carbon film in the grooves of first substrate. Thus, the service life of the substrate made of a polyimide resin is enhanced. The cooling performance is enhanced, due to the increased fluidity of the working fluid.
According to a sixth aspect of the present invention, there is provided a method of producing a cooling device which comprises the steps of forming a first substrate having open grooves constituting a heat pipe formed therein, the open grooves excluding at least the open groove positioned in correspondence to a wick, forming a second substrate made of a metal or a material having a thermal conductivity substantially equal to that of a metal, the second substrate having at least the groove for the wick formed on the surface thereof, joining a first surface of the first substrate to a lid-substrate to form a flow-path for a working liquid, incorporating the second substrate into a third substrate so as to be exposed to the surface of the third substrate, and joining the surface of the third substrate to the second surface of the first substrate.
Thereby, the cooling device having the above-described structure can be produced efficiently and securely.
Preferably, the method further comprises the steps of: forming a fourth substrate made of a metal or a material having a thermal conductivity substantially equal to that of a metal, the fourth substrate having at least a groove for a condenser formed on the surface thereof, and incorporating the fourth substrate into the third substrate so as to be exposed to the surface of the third surface. Thereby, the heat-radiating means (condenser) can be efficiently incorporated in the device.
Preferably, the step of forming the flow-path for a working fluid includes a step of forming a diamond-like film on the surface of the flow-path. Thereby, the cooling device of which the substrates have enhanced durability and cooling performance is produced.